The present invention relates to semiconductor integrated circuits. More particularly, the present invention provides a technique, including a method and structure, for forming an isolation region or film in a semiconductor device. In an embodiment, the present invention provides a novel isolation technique by which semiconductor devices can be highly integrated for sub-micron sized devices.
In order to increase the degree of integration of semiconductor devices, it is desirable to reduce dimensions of active device elements, and also reduce dimensions of width and area of isolation regions, which are formed between the active device elements. Because the amount of reduction roughly determines, for example, a memory cell size, the isolation technique employed plays an important role in highly integrated memory cells.
Industry has used or proposed a variety of techniques to form isolation regions for a semiconductor device. As merely an example, conventional methods of forming isolating films include, among others, a local oxidation of silicon, which is commonly termed the LOCOS process, by which a field oxide is thermally grown in exposed regions, and a mask made of silicon nitride covers regions for active devices. The LOCOS process, however, often has significant problems such as a commonly known problem called xe2x80x9cbird""s beakxe2x80x9d which reduces the size of active regions. The bird""s beak often makes high integration of semiconductor devices difficult. In addition, LOCOS is often not a xe2x80x9cgoodxe2x80x9d isolation between active devices since the available volume of field oxide under, for example, the silicon surface is no more than 40-45% of its total volume.
In order to solve some of the aforementioned limitations, an alternative technique has been used, which is commonly termed trench isolation. Trench isolation is formed by etching grooves or slits in a semiconductor material by way of etching techniques, e.g., reactive ion etching and others. The grooves or slits are filled with a dielectric material or isolating material such as silicon dioxide or the like to isolate active regions in the semiconductor substrate. The trench process has been introduced by virtue of its advantages in that the field oxide is fully available and has no bird""s beak. The trench process, however, is very complicated. There has also been developed a modified LOCOS process in which the bird""s beak is shortened by forming a nitride spacer at the side wall of an element isolating region and a field oxide is grown in a shallow recess formed in a semiconductor substrate. The modified LOCOS process, however, also has severe limitations.
From the above, it is seen that a technique for improving isolation in semiconductor integrated circuits is highly desirable.
According to the present invention, a technique, including a method and structure, for isolating a device region is provided. In an exemplary embodiment, the present invention provides an isolation technique with selective temperature control to avoid problems of conventional techniques.
In accordance with an aspect of the present invention, a method for forming an element isolation film or region in a semiconductor device is provided. The method includes, among others, a step of providing a semiconductor substrate. The method also includes a step of constructing an element isolation mask on a surface of the semiconductor substrate. A spacer at a side wall of the element isolation mask is formed. The entire substrate, including isolation mask and side wall, is oxidized where an exposed region of the semiconductor substrate grows an oxide, e.g., silicon dioxide, thermal oxide. The method includes a step of removing the oxide to form a recessed region in the semiconductor substrate. A field oxide is formed through break-through field oxidation (hereinafter referred to as xe2x80x9cBTFOXxe2x80x9d) and high temperature field oxidation (hereinafter referred to as xe2x80x9cHTFOXxe2x80x9d). BTFOX and HTFOX will be described in more detail below.
Numerous advantages are achieved by way of the present invention over pre-existing techniques. As merely an example, the present invention provides a semiconductor device with a field oxide that is formed in a recess in a field region of a semiconductor substrate by a combination of BTFOX and HTFOX, which are relatively easy to implement. Additionally, the present invention overcomes one or more of the limitations encountered in conventional LOCOS using, for example, a novel method for forming an element isolation film or isolation region of a semiconductor device, which can take advantage of high temperature field oxidation without creating a field oxide ungrowth (herein xe2x80x9cFOUxe2x80x9d) phenomenon. Furthermore, the present invention provides a semiconductor device having an FOU-free element isolation film formed through high temperature field oxidation. These and other benefits are advantages are described throughout the present specification and more particularly below.
The present invention achieves these benefits in the context of known process and product technology. The above benefits and/or aspects of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings.